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Hydrogeology of an Alpine Valley, southeastern Hydrogeology of an Alpine Valley, southeastern British Columbia British Columbia –– Implications for Coalbed Implications for Coalbed
Methane Exploration and Development Methane Exploration and Development
SHANE M. HARRISON , M.Sc., P. Geol., P. Geo.SH Consulting Services
APPROACH / OUTLINEAPPROACH / OUTLINE
PART I PART I –– OverviewOverview
nn Location / Physical SettingLocation / Physical Settingnn Stratigraphy / HydrostratigraphyStratigraphy / Hydrostratigraphynn Data CollectionData Collection
•• PressurePressure•• ““TransmissivityTransmissivity””
(permeability)(permeability)•• Water ChemistryWater Chemistry
nn Sampling Locations / Sampling Locations / Instrumentation Instrumentation
PART II PART II –– GROUNDWATER FLOWGROUNDWATER FLOW
nn Flow SystemFlow System–– Physical ConstraintsPhysical Constraints–– Hydrochemical ConstraintsHydrochemical Constraints
nn Numerical ModelingNumerical Modeling
PART III PART III –– Exploration / Production Exploration / Production ConsiderationsConsiderations
nn Production Production –– e.g. Well Spacing e.g. Well Spacing nn Gas Content / Gas originGas Content / Gas origin
APPROACH / OUTLINEAPPROACH / OUTLINE
PART I PART I –– OverviewOverview
nn Location / Physical SettingLocation / Physical Settingnn Stratigraphy / HydrostratigraphyStratigraphy / Hydrostratigraphynn Data CollectionData Collection
•• PressurePressure•• ““TransmissivityTransmissivity””
(permeability)(permeability)•• Water ChemistryWater Chemistry
nn Sampling Locations / Sampling Locations / Instrumentation Instrumentation
PART II PART II –– GROUNDWATER FLOWGROUNDWATER FLOW
nn Flow SystemFlow System–– Physical ConstraintsPhysical Constraints–– Hydrochemical ConstraintsHydrochemical Constraints
nn Numerical ModelingNumerical Modeling
PART III PART III –– Exploration / Production Exploration / Production ConsiderationsConsiderations
nn Production Production –– e.g. Well Spacing e.g. Well Spacing nn Gas Content / Gas originGas Content / Gas origin
GENERAL LOCATION MAPGENERAL LOCATION MAP
STUDYSTUDYLOCATIONLOCATION
COAL FIELDS COAL FIELDS LOCATION MAP LOCATION MAP
(general)(general)
Alberta Alberta ––British Columbia borderBritish Columbia border
PHYSICAL SETTINGPHYSICAL SETTING
nn ALPINE VALLEY, FRONT RANGES, ROCKY ALPINE VALLEY, FRONT RANGES, ROCKY MOUNTAINSMOUNTAINS
–– ELEVATIONSELEVATIONS•• LOWLAND (VALLEY) LOWLAND (VALLEY) -- 1550 1550 -- 1600 m1600 m•• UPLAND UPLAND -- 2200 2200 -- 2800 m2800 m
nn RUGGED TERRAIN WITH FEW DATARUGGED TERRAIN WITH FEW DATA
2200 - 2800 m asl1550 m asl
1600 m asl
Rocky Mountains Elk Valley
Approx. 6 km
Approx. 3-4 km
N
bridge
PHYSICAL / CHEMICAL PHYSICAL / CHEMICAL HYDROGEOLOGY HYDROGEOLOGY
nn STRATIGRAPHY DEFINES MAJOR STRATIGRAPHY DEFINES MAJOR HYDROSTRATIGRAPHIC UNITS:HYDROSTRATIGRAPHIC UNITS:
–– CARBONIFEROUSCARBONIFEROUS•• LIMESTONE;SOME DOLMITE AND SANDSTONELIMESTONE;SOME DOLMITE AND SANDSTONE
–– TRIASSICTRIASSIC•• SANDSTONE AND SHALESANDSTONE AND SHALE
–– JURASSICJURASSIC•• SHALE AND SANDSTONE/SILTSTONESHALE AND SANDSTONE/SILTSTONE
–– JURASSIC/CRETACEOUSJURASSIC/CRETACEOUS•• SANDSTONE , SILTSTONE, SHALES, COAL (Mist SANDSTONE , SILTSTONE, SHALES, COAL (Mist
Mountain Formation)Mountain Formation)•• Coals are subCoals are sub--bituminousbituminous
GEOLOGICALMAP
• Syncline
• Bourgeau Thrust
• Lewis Thrust
Bourgeau Thrust
Lewis Thrust
CROSS-SECTION
Syncline:
• Plunges north at shallow angle• Open to slightly overturned• Axial plane strikes at ≈160º; dips westerly
Groundwater Surface Water SamplingSamples collected of surface and formation water (groundwater) for chemical analyses from:• Seeps, streams, open wells, ponds, monitoring wells / piezometers
Hydraulic DataHydraulic conductivity and water level data from:• Open wells, monitoring wells / piezometers
Hydrological Data
• Gauging stations, streams, seeps, ponds
DATA COLLECTION
Site 1
Site 2
Elk RiverValley
open wells
streams
ponds
seeps
CBM test
guaging st.
Sample / Monitoring Locations(Plan View)
SAMPLINGSAMPLINGINSTRUMENTATION SITES 1 and 2INSTRUMENTATION SITES 1 and 2
(CROSS(CROSS--SECTION SITE 1)SECTION SITE 1)
VE = .65x
APPROACH / OUTLINEAPPROACH / OUTLINE
PART I PART I –– OverviewOverview
nn Location / Physical SettingLocation / Physical Settingnn Stratigraphy / HydrostratigraphyStratigraphy / Hydrostratigraphynn Data CollectionData Collection
•• PressurePressure•• ““TransmissivityTransmissivity””
(permeability)(permeability)•• Water ChemistryWater Chemistry
nn Sampling Locations / Sampling Locations / Instrumentation Instrumentation
PART II PART II –– GROUNDWATER FLOWGROUNDWATER FLOW
nn Flow SystemFlow System–– Physical ConstraintsPhysical Constraints–– Hydrochemical ConstraintsHydrochemical Constraints
nn Numerical ModelingNumerical Modeling
PART III PART III –– Exploration / Production Exploration / Production ConsiderationsConsiderations
nn Production Production –– e.g. Well Spacing e.g. Well Spacing nn Gas Content / Gas originGas Content / Gas origin
CONCEPTUAL MODEL OF FLOW CONCEPTUAL MODEL OF FLOW PHYSICAL HYDROGEOLOGYPHYSICAL HYDROGEOLOGY
M. King Hubbert (1940)
Classic Model Of Upland To Lowland Flow
Joseph Toth (1963)
Regional Flow Systems
UPLAND UPLAND –– LOWLAND FLOWLOWLAND FLOW
“ALTITUDE EFFECT”δ18O and δ2H (data from Yonge et al., 1989)
δ2H = -75.67 – 0.015 (elev.) – 0.08 (dist.)δ18O = -10.25 – 0.002 (elev.) – 0.009 (dist.)
““lighter or depletedlighter or depleted”” δδ 1818O / O / 22HH
Isotopic fractionationIsotopic fractionation
““heavyheavy”” isotopesisotopes
““enrichedenriched”” δδ 1818O / O / 22HH
HYDROCHEMISTRYHYDROCHEMISTRYCONSTRAINTS ON FLOWCONSTRAINTS ON FLOW
nn APPROXIMATELY 50 SAMPLES COLLECTED APPROXIMATELY 50 SAMPLES COLLECTED FROM:FROM:
–– MONITORING WELLSMONITORING WELLS•• COMPLETED FROM ABOUT 50 TO 200 m DEPTHCOMPLETED FROM ABOUT 50 TO 200 m DEPTH
–– OPEN WELLS (UP TO 600 m DEPTH)OPEN WELLS (UP TO 600 m DEPTH)–– SEEPSSEEPS–– PONDSPONDS–– STREAMSSTREAMS–– ELK RIVERELK RIVER
“ALTITUDE EFFECT” δ18O and δ2H
GROUNDWATER GROUPS GROUNDWATER GROUPS -- STUDY AREASTUDY AREA
TDS
SYNTHESISSYNTHESIS
nn GROUP A GROUNDWATER (GROUP A GROUNDWATER (““freshfresh””))•• HIGH TRITIUM; ENRICHED HIGH TRITIUM; ENRICHED δδ1818O/O/δδ22HH•• LOW TDSLOW TDS
–– LOW HCOLOW HCO33--
nn GROUP B GROUNDWATER (GROUP B GROUNDWATER (““evolvedevolved””))•• LOW OR NO TRITIUM; DEPLETED LOW OR NO TRITIUM; DEPLETED δδ1818O/O/δδ22HH•• HIGH TDSHIGH TDS
–– HIGH HCOHIGH HCO33-- ENRICHED IN ENRICHED IN δδ1313CC
nn INTERMEDIATEINTERMEDIATE–– TRANSITIONAL / MIXED COMPONENTTRANSITIONAL / MIXED COMPONENT
HYDROCHEMICAL CONSTRAINTS ON FLOWDepleted δ18O and δ2H
FLOW SYSTEM FLOW SYSTEM MATHEMATICAL REPRESENTATIONMATHEMATICAL REPRESENTATION
nn 33--D FINITE ELEMENT D FINITE ELEMENT –– Watflow 3Watflow 3--D (Molson et al.)D (Molson et al.)
nn BOUNDARY CONDITIONSBOUNDARY CONDITIONS•• Water table is fixed (specified head)Water table is fixed (specified head)•• Lewis and Bourgeau thrusts assumed Lewis and Bourgeau thrusts assumed
impermeable (no flow)impermeable (no flow)
nn SOLVE FOR STEADYSOLVE FOR STEADY--STATE FLOW:STATE FLOW:
0)()()( =++dzdhKz
dzd
dydhKy
dyd
dxdhKx
dxd
NUMERICAL SIMULATION
Hydraulic Parameters:
• equiv. porous media• K values • porosity values• anisotropy ratios
Model Domain:Heterogeneous and anisotropic conductivity field with 420,000 elements (3-D domain)
Boundary Conditions:
• specified head• “no flow”
RESULTS - NUMERICAL SIMULATION
SO WHAT IS THE SO WHAT IS THE APPLICATION!!!!APPLICATION!!!!
APPROACH / OUTLINEAPPROACH / OUTLINE
PART I PART I –– OverviewOverview
nn Location / Physical SettingLocation / Physical Settingnn Stratigraphy / HydrostratigraphyStratigraphy / Hydrostratigraphynn Data CollectionData Collection
–– PressurePressure–– ““TransmissivityTransmissivity”” (permeability)(permeability)–– Water ChemistryWater Chemistry
nn Sampling Locations / Sampling Locations / Instrumentation Instrumentation
PART II PART II –– GROUNDWATER FLOWGROUNDWATER FLOW
nn Flow SystemFlow System–– Physical ConstraintsPhysical Constraints–– Hydrochemical ConstraintsHydrochemical Constraints
nn Numerical ModelingNumerical Modeling
PART III PART III –– Exploration / Production Exploration / Production ConsiderationsConsiderations
nn Production Production –– e.g. Well Spacing e.g. Well Spacing nn Gas Content / Gas originGas Content / Gas origin
CBM PRODUCTION
nn DECREASE DECREASE RESERVOIR RESERVOIR PRESSURE (for an PRESSURE (for an underunder--saturated initial saturated initial condition)condition)
–– METHANE DESORBS METHANE DESORBS FROM THE COAL FROM THE COAL STRUCTURESTRUCTURE
–– WATER AND GAS FLOW WATER AND GAS FLOW TOWARD THE TOWARD THE PRODUCTION WELLPRODUCTION WELL
waterflow
water & dissolvedmethane
gas & waterflow
water and gas flowingwater flowing
DISTANCE FROM THE BOREHOLE
drawdownoriginal potentiometric surface
discharge
STAGE 1 STAGE 2
STAGE 3
PRESSURE
CBM PRODUCTIONCBM PRODUCTION
CBM / WATER PRODUCTIONCBM / WATER PRODUCTION
DEWATERING STABLEPRODUCTION
DECLININGPRODUCTION
METHANE
PROD.
TIME
WATER
3-D FLOWMODELING
CBM DEVELOPMENT
CBM DEVELOPMENTCBM DEVELOPMENTDepressurizationDepressurization
•How many wells?•Spacing?•How much water?
““BULKBULK--ROCKROCK”” RESPONSE TO RESPONSE TO DEPRESSURIZATIONDEPRESSURIZATION
““Real WorldReal World””
nn Borrow methods from the Water Well Borrow methods from the Water Well IndustryIndustry
Pumping Test: (65 mPumping Test: (65 m33/day for 15 days) /day for 15 days) –– drawdown is proportional to drawdown is proportional to ““QQ”” (pumping (pumping
rate)rate)–– drawdown is inversely proportional to drawdown is inversely proportional to
hydraulic conductivity (hydraulic conductivity (““KK”” or or ““TT””))
DRAWDOWNDRAWDOWN22,000 minutes (15 days) Q = 65 m22,000 minutes (15 days) Q = 65 m33/day/day
VE = .65x
DRAWDOWN SCHEMATICDRAWDOWN SCHEMATIC
Steep and narrow drawdown cone
1. steep and narrow→ low perm
2. volume of rock impacted by pressure-pulse is small
CBM EXPLORATION
Zone(s) of most significant overZone(s) of most significant over--pressuring?pressuring?
CBM EXPLORATION (con’t)
EFFECTS ON FLOW SYSTEM EFFECTS ON FLOW SYSTEM e.g. Water Table Fluxe.g. Water Table Flux
Other Data:
• Isotopic data• Stream flow• Monitoring well
Gas Origin???Gas Origin???
EXPLORATION: Biogenic ProcessesEXPLORATION: Biogenic Processes
EXPLORATION: Geochemical Markers EXPLORATION: Geochemical Markers
nn δδ1313C C –– DIC becomes enriched (+35 DIC becomes enriched (+35 ‰‰) ) nn DIC concentration (mg/L) increasesDIC concentration (mg/L) increasesnn Methane concentration (mg/L) increases Methane concentration (mg/L) increases
diagram shows as DIC diagram shows as DIC ↑↑ δδ1313CCDICDIC ↑↑ and CHand CH44 ↑↑
TYPICAL OF METHANOGENIC ENVIRONMENTS!!
DIC, METHANE, δ13CDICGROUP B
GROUP A
EFFECT ON MAJOR ION EFFECT ON MAJOR ION GROUNDWATER CHEMISTRYGROUNDWATER CHEMISTRY
Carbon dioxide is generated through methanogenesis dissociates into the groundwater resulting in high DIC concentrations (1250 + mg/L)
SUMMARY AND CONCLUSIONSSUMMARY AND CONCLUSIONS
nn Setting Setting Alpine valley southeastern British ColumbiaAlpine valley southeastern British Columbia
Relief: 1550 Relief: 1550 –– 2800 m2800 m
Structurally relatively complexStructurally relatively complex
nn DataDataCollected from wells, seeps, streams, pondsCollected from wells, seeps, streams, ponds
Detailed hydraulic, geochemistry and flow Detailed hydraulic, geochemistry and flow
SUMMARY AND CONCLUSIONSSUMMARY AND CONCLUSIONSconcon’’tt
nn Gas OriginGas OriginPredominantly biogenic (COPredominantly biogenic (CO22 reduction)reduction)Generated by active groundwater flowGenerated by active groundwater flow
nn Flow and Flow ModelingFlow and Flow ModelingConstrain flow chemically and physicallyConstrain flow chemically and physically
Represent flow mathematicallyRepresent flow mathematically
Simulations useful for early stage evaluations of Simulations useful for early stage evaluations of development / exploration scenarios (must development / exploration scenarios (must understand limitations of models)understand limitations of models)
THANK YOU!THANK YOU!
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